Patients with essential hypertension may be categorized as salt-sensitive or non salt-sensitive, depending on whether blood pressure increases or remains unchanged when sodium intake is increased from 9 to 249 mEq/day. Adrenergic and dopaminergic function was evaluated in these two subsets of patients and correlated with sodium excretion and blood pressure when sodium intake was 9 mEq/day and after it had been increased to 249 mEq/day. The salt-sensitive patients did not show the suppression of plasma and urinary norepinephrine that normally occurs when a low sodium intake is changed to a high sodium intake. This persistence of increased sympathetic activity during a high sodium intake may impair sodium excretion and be responsible for the increase in blood pressure in the salt-sensitive patients. In non salt-sensitive patients plasma and urinary norepinephrine decreased by 31% and 25%, respectively, during high salt intake; urinary dopamine was high and did not increase further. The increase in dopaminergic activity was associated with less sodium retention and a more rapid "escape" from the sodium load than was the case in the salt-sensitive patients. The increased dopaminergic activity may be a factor in the hypertension of non salt-sensitive patients.